Glaucoma is a term which refers to a family of conditions which cause optic nerve damage. Glaucoma is currently the leading cause of blindness and continues to cause blindness in around 10% of even those patients who receive the most up to date treatment [1]. There are currently strategies for managing Glaucoma including eye drops and surgeries, but often the eye drops can cause problems ranging from eye irritation to severe heart problems [2]. The surgeries used to treat glaucoma are often successful, but bring the usual surgical risks, and often treat the problem only for a short time.
What scientists now believe causes the most prevalent type of glaucoma is an excess of intraocular pressure (IOP) which presses on, then damages the optic nerve [2]. Fluid is pumped into the anterior chamber of the eye to, among other things, clean the lens. The fluid and is then drained out through the drainage tissues at the junction of the cornea and iris in the region of the eye known as the limbus [3]. An excess of the aqueous humor in the eye could be caused by a combination of the ciliary body producing too much fluid, or too much resistance to aqueous humor drainage out of the eye. Existing medical and surgical treatments reduce IOP to non-damaging levels by targeting either the drainage or production of aqueous humor
Current treatment methods for reducing intraocular pressure in glaucoma patients incur unacceptable side effects or provide only temporary relief of symptoms for the chronic disease [2]. There is a need to develop a method to permanently reduce the intraocular pressure in the eye of all patients with glaucoma to a normal level (15.5 mmHg) without causing unacceptable side effects [4].
This book chapter describes what glaucoma is and the two different glaucoma types, open-angle and closed-angle glaucoma. It also describes the necessary treatments for patients suffering from glaucoma. This provides a good starting source for learning the basics of glaucoma.[7]
This article explains normal and abnormal operating conditions of the eye with respect to the intraocular pressure. The steady state operations of the IOP is detailed at 10-20 mmHg. This also explores into what determines the IOP levels and what can disrupt the normal pressure. This entry details routine dynamics of the fluid production and flow. It also tells how various conditions and stimuli can affect the IOP.[8]
This study uses electrical stimulation on the ciliary muscle. These researchers found using pulses up to 15 ms long with a current amplitude up to 10 mA for three to seven minutes using a lens with four electrodes placed on the eyeball. Gradual improvements visual and hydrodynamic parameters were seen by the end of the follow-up in six months. After ten sessions on transscleral stimulation IOP decreased by 16%. [9]
This patent puts forth a method to prevent presbyopia and glaucoma through ciliary body stimulation. This method uses low-voltage dc pulses transmitted to the ciliary body though electrodes attached to lenses placed over both eyes. The lenses are set 2-5 mm from the corneal limbus. [10]
This source is a patent for a system that can be used to treat ocular misalignment. The treatment is using electrical stimulation of ocular recti using an implantable unit. The stimulation signal is a periodically interrupted train of pulses, with 50 to 100 pulses per minute. [11]
This patent provides a system for treating open angle glaucoma and presbyopia through electrical stimulation of the ciliary muscle. This implant used delivers signals to the ciliary muscle that widens the interbecular spaces to facilitate outflow of aqueous fluid from the eye and widens the lense, thereby lowering IOP. [12]
Within the eye, there is a smooth-muscle tissue called the ciliary muscle, which is part of the ciliary body. It has two different orientations of the muscle with separate functions. The circular muscle tissue controls the shape of the lens in the eye. Changing the shape of the lens changes the focus of the eye so that the image will always be clear on the back of the retina. The longitudinal muscle tissue controls the configuration of the trabecular meshwork. The aqueous humor is secreted by the ciliary body. It is secreted into the posterior chamber of the eye between the iris and lens. It washes over the lens and then moves through the pupil into the anterior chamber. Ultimately, much of the aqueous humor leaves the eye through the trabecular meshwork and Schlemm's canal drainage tissues. Some aqueous humor leaves the eye through the uveoscleral drainage pathway, a process that is also modulated by the ciliary muscle. Aqueous humor production, flow and drainage are important for nourishing the front of the eye, removing metabolites and normal vision.
In a patient with glaucoma, the aqueous humor builds up in the eye. This can be due to the blocking or a slowing of the drainage of the aqueous humor in the trabecular meshwork. As the excess fluid builds in the eye, it increases the intraocular pressure. As this pressure increases, it causes the optic nerve to get damaged. If left untreated, the pressure does so much damage to the optic nerve that it will eventually lead to blindness [13].
There are actually multiple types of glaucoma. Open-Angle glaucoma is where the aqueous humor does not drain as quickly due to abnormal resistance in the trabecular meshwork and Schlemm's canal pathway. The increase in pressure is usually a slow process. Angle-Closure glaucoma is where the aqueous humor does not drain from the eye because of a sudden blockage of the trabecular network by the iris. This causes a sudden spike in the intraocular pressure and is considered an emergency. Congenital glaucoma is a birth defect caused by abnormal eye development. Secondary glaucoma is caused by external factors such as drugs, disease, or trauma. Open-Angle glaucoma is the most common form of glaucoma and has a clear genetic component [13].
Symptoms vary depending on the type of glaucoma. Open-angle glaucoma generally does not exhibit any symptoms. When vision starts to decrease, severe damage has already been done to the optic nerve. Angle-close glaucoma has symptoms such as eye pain, clouded vision, nausea, rainbow halos around lights, and red or swollen eyes. Congenital glaucoma may go unnoticed for a while. A child may get cloudy eyes, an enlargement of one or both eyes, red eye, sensitivity to light, or tearing [13].
As one of the most prevalent causes of blindness across the globe, glaucoma affects around 60.5 million people (as of 2010) [14] with an incidence of 7 million new cases each year (as of 2009). Within the U.S. open-angle glaucoma, the most common subtype in the glaucoma family affects around 2.5 million people [15]. The populations of patients with glaucoma or high IOP (ocular hypertension, OHT) are both predicted to grow steadily over the next several years. From FIGS. 8 and 9 it can be seen that by 2016 the prevalences are expected to be 3.1 million and 5.0 million for glaucoma and OHT respectively, with compound annual growth rates of about 1.6% for both populations. From this analysis it is attractive to target the IOP regulating therapy to the OHT population as well as the traditional glaucoma population.
The cost of pharmaceutical treatment of glaucoma has been thoroughly studied revealing that even generic medications create a cost issue in the treatment. Other costs associated with glaucoma include surgeries, doctors appointments, procedures and especially loss of vision all result in loss of productivity for patients due to absenteeism. One study estimates this cost to the U.S. economy to be greater than $3 billion [15]. This cost has potential to be recovered by a more effective way of monitoring and treating glaucoma.
The new technologies being developed include both methods in identifying and treating patients with glaucoma. There is new research on using oximetry to determine if there are differences between the oxygen content in the eye of patients with glaucoma compared to patients without glaucoma [21]. Our design is used as a treatment for glaucoma while this research is to try and identify patients with glaucoma so there is no conflict with our design.
Emerging technology can be found in ways to treat glaucoma. There is research on using an injection of bevacizumab after implanting a valve in the eye to try and improve the efficacy of the implant. Bevacizumab is a drug that decreases vascular endothelial growth factor-A. By injecting the drug into the eye after an implant they hope to decrease the scar tissue that forms after the surgery to avoid a fibrous capsule forming around the implant. There is also research on using statins as a treatment for glaucoma [22]. These statins inhibit HMG-CoA reductase catalyzed transformation of HMG-CoA to mevalonic acid. Another drug treatment method for glaucoma is the use of thrombin-derived peptides [23]. Our design does not use drugs to treat glaucoma so there is no conflict with our design.
There are also several different patents for implants and devices to treat glaucoma. There is a design for a new tube to be used as a valve to improve the drainage system as a treatment for open-angle glaucoma. This is designed to better allow fluid flow through the implant and into Schlemm's canal [24]. The design can be seen in FIG. 1.
Another implant is a plate designed to treat angle-closure glaucoma by placing the plate partially in Schlemm's canal. This design tried to correct the errors in other implants for angle-closure glaucoma by allowing good flow into Schlemm's canal and also keeping the surrounding tissue around the implant safe from high flow rates [25]. A drawing of this plate can be seen in FIG. 2.
A new idea is to use a pump in conjunction with an implanted valve to aid in the removal of the aqueous humor. This would increase the outflow of the fluid. Reverse flow of the fluid is prevented by using one-way valves [26]. FIG. 3 shows a diagram of this idea.
There is also a patent on a device that aids in trabeculotomy surgeries. This device includes a footplate to penetrate into Schlemm's canal, an infusion system to allow fluid to flow out to a collection plate during the surgery, and an aspiration system to remove tissue or bubbles and is directly connected to the cutting blade or other tissue removal system [26]. A drawing of the device can be seen in FIG. 4.
Another design is for scleral implants that aid in the drainage of the aqueous humor. This implant purportedly relieves intraocular pressure by exerting an outward pressure on the sclera to restore proper outflow of the aqueous humor. It also allows for a drug delivery system not provided in other ocular implants [27]. FIG. 5 shows a drawing of these scleral implants.
These ideas are improvements on existing methods of treating and all have an intraocular component. Nevertheless, there remains a need for cost effective strategies for the treatment of glaucoma. A big gap in the current solutions is for a treatment that is relatively low risk but also convenient for the patient. What exists now are solutions that are either low risk (topical agents) or convenient for the patient long-term (surgery), but not both. There is also a need for a method that is more biocompatible with the eye and has less side effects. Almost all of the current treatments result in a chance of some mild to serious side effects. This risk becomes increasingly acceptable for a patient as they come closer to blindness, but an ideal solution will provide relief of elevated IOP with minimal to no side effects. Finally, the current treatments have little adjustability for treating patients individually and none have feedback mechanisms based on IOP.
Current pharmacological and surgical methods for reducing intraocular pressure in glaucoma and ocular hypertensive patients present high risk of complications or provide only acute relief of symptoms for the chronic disease.
There is a need to develop a method to chronically reduce IOP of all patients with glaucoma or ocular hypertension to a normal level without causing unacceptable side effects.
While many surgical and chemical solutions exist, the other categories are mainly filled with solutions that are not currently on the market. The two biggest approaches to glaucoma treatment at the moment are surgeries to open channels in the eye, or eye drops to regulate fluid flow, and other types of intervention (i.e. electrical, or implanted devices) have not yet successfully been brought to market. This suggests that a solution from one of these other areas has the potential to avoid some of the limitations of current glaucoma treatment (i.e. the need for repeated surgeries, or the unacceptable side effects of eye drops [38]).
Current pharmacological and surgical methods for reducing intraocular pressure in glaucoma and ocular hypertensive patients present risk of complications or provide only temporary relief of symptoms for the chronic disease.
There is a need to develop a method to chronically reduce IOP of all patients with glaucoma or ocular hypertension to a safe level without causing unacceptable side effects.